Method for preparing diethylketone with good selectivity

ABSTRACT

This invention relates to a method to produce diethylketone, with superior selectivity, from ethylene and carbon monoxide under pressure in an alcohol-water system solvent with a rhodium compound catalyst or a catalyst system comprising a rhodium compound and organophosphorus compounds having the infrared A1 carbonyl stretching frequency of Ni(CO)3L (L is an organophosphorus compound) in methylene chloride in accordance with the definition by Tolman in the range above 2066 cm 1.

United States Patent [191 Hara [ Dec. 2, 1975 [75] Inventor:

[73] Assignee: Nippon Oil Company Ltd., Tokyo,

Japan [22] Filed: Apr. 23, 1973 [2]] Appl. No.: 353,529

Hajime Hara, Fujisawa, Japan [30] Foreign Application Priority Data Apr. 26, 1972 Japan l. 47-41862 [56] References Cited UNITED STATES PATENTS 2,839,580 1/1956 Hughes et al. 260/597 R 3,040,090 6/1962 Alderson ct al 260/597 R 3,168,553 2/1965- Slaugh 260/597 R 3,257,459 l/l966 Swakon ct al 260/597 R Primary Examiner-James 0. Thomas. Jr.

Assistant E.\ aminerJames H. Reamer Attorney, Agent, or Ft'rm-Ostr0lenk, Faber, Gerb & Soffen [57] ABSTRACT This invention relates to a method to produce diethylketone, with superior selectivity, from ethylene and carbon monoxide under pressure in an alcoholwater system solvent with a rhodium compound catalyst or a catalyst system comprising a rhodium compound and organophosphorus compounds having the infrared A carbonyl stretching frequency of Ni(- CO) L (L is an organophosphorus compound) in methylene chloride in accordance with the definition by Tolman in the range above 2066 cm".

9 Claims, No Drawings METHOD FOR PREPARING DIETI-IYLKETONE WITH GOOD SELECTIVITY This invention relates to a method for synthesizing diethylketone by reacting ethylene with carbon monoxide.

It is known well that in the x0 reaction, diethylketone is produced as a by-product when ethylene is employed as the olefin. Many attempts have heretofore been made to selectively synthesize diethylketone, and in most of these attempts, cobalt or rhodium compounds have been used as a catalyst as in the 0x0 reaction. For example, see Italian Pat. No. 475,040 and JACS, 74,4496 (1952). In these references, ethylene is reacted with carbon monoxide in the presence of an al coholic solvent with a cobalt catalyst to obtain diethylketone, but a great amount of the catalyst and a high pressure over 200 Kglcm are required, and the formation of a large amount of propionaldehyde and esters of propionic acid, etc., reduces the selectivity to diethylketone.

US. Pat. No. 2,839,580 discloses the fact that the re action between ethylene and carbon monoxide is carried out effectively in the presence of alcohol as a solvent to obtain diethylketone with remarkably little catalyst used. However, a total pressure as high as 250 Kg/cm is required. Although a comparatively small amount of propionaldehyde is formed, non-volatile matters as bottoms of 25% by weight to diethylketone on fractional distillation of the reaction product remains. This shows that a large amount of compounds with high boiling points are formed in the reaction.

In the U.S. Pat. No. 3,040,090, the reaction between ethylene and carbon monoxide is performed in the presence of water or alcohol as a solvent by using a catalyst which is a chelate of noble metals of group VIII such as rhodium and ruthenium. In this work, there is necessitated a reaction pressure as high as 1,000 Kg/cm and the large amount of high boiling compounds such as 3,6-octadiene and others formed makes the selective production of diethylketone difficult.

The US. Pat. No. 3,257,459 describes that diethylketone is selectively produced when the ethylene-carbon monoxide reaction is conducted in an aqueous solvent with a cobalt catalyst, provided there is also present an organic base such as tetramethylquanidiene. A maximum pressure above 350 Kg/cm and a large quantity of catalyst are required.

There are some cases in which ethylene is reacted with carbon monoxide under a reaction condition of a lower partial pressure of hydrogen. See the US. Pat. No. 2,473,995 and the Germman Pat. No. 1,793,320. Both of the patents require a high pressure more than 250 Kglcm and the selectivity to diethylketone is also low. In the US. Pat. No. 2,699,453 and British Pat. No. 663,089, diethylketone is obtained by the reaction be tween ethylene, carbon monoxide and hydrogen in the gas phase at a pressure up to about 100 Kg/cm in the presence of a cobalt catalyst supported on a carrier, but

' the content of diethylketone in the liquid reaction mixture obtained is 85% by weight maximum, and the productivity is very low as is clear from the space velocity of about 100; space velocity is herein defined as volume of gaseous reactants per volume of catalyst per hour.

As is described above, the prior art processes do not give satisfactory results in the industrial production of 2 diethylketone, because in order to attain a pertinent conversion rate of ethylene, they require a large amount of catalyst, a small space velocity and/or a high pressure as high as more than 200 Kglcm In addition, propionaldehyde, esters of propionic acid and/or high boiling substances are largely formed as a by-product. In case of using a cobalt catalyst, troublesome operations are frequently required for the circulation of the catalyst solution and the recovery and regeneration of the catalyst owing to the instability of its carbonyl complex, and therefore a great loss of the catalyst results.

Now it has been found that diethylketone is synthesized with a large reaction rate and with a good selectivity by reacting ethylene with carbon monoxide in an alcohol-water system solvent by using a rhodium compound as a catalyst under conditions of a comparatively low pressure. It has also been found that the addition of an alkylphosphine, aryl phosphine, alkylphosphite or arylphosphite, etc. to the catalyst system above further increases the reaction rate, and that a specific phosphorous compound such as triphenylphosphine functions to depress the formation of high boiling compounds such as polyketones and others.

This invention has been completed on the basis of the finding of the abovefacts.

An object of this invention is to provide a novel method for producing advantageously and selectively diethylketone from ethylene and carbon monoxide on an industrial scale.

Another object of this invention is to provide a novel catalyst comprising rhodium compounds or a combined catalyst system of a rhodium compound and an organophosphorous compound suitable for the selection production of diethylketone in a high yield and with comparatively simple operations.

And further objects of this invention will be seen from what will be described more in detail hereinunder.

A first point of this invention resides in that when an alcohol-water containing solvent is used, the reaction rate of diethylketone synthesis from ethylene and carbon monoxide and the selectivity to diethylketone are greatly improved compared with the reaction in an alcohol or a water solvent alone. Further, the hydrogen necessary for the forming of diethylketone is made up from the water, so waste of expensive alcohol can be avoided.

A second point of this invention is in that the reaction rate of forming diethylketone from ethylene and carbon monoxide is remarkably increased by addition of organophosphorous compounds such as (CH C I-I P, (C H P, (CH CH O) P, (CI-I C H O) P and (C H O) P to rhodium compounds.

A third point of this invention exists in that the forming of a high boiling compound such as polyketones is remarkably depressed in the reaction of ethylene and carbon monoxide using a catalyst system comprising a rhodium compound and an organophosphorous compound Such as (CH3C6H4)3P, (C6H5)2P, (CGH5CH2) 6 5)2 a (C6H4F) (C6H5)2P, a 5h and (CI-I 0) (C 11 added thereto, and that diethylketone is selectively synthesized.

A fourth point of this invention lies in that when the reaction between ethylene and carbon monoxide is conducted by using said catalyst and said solvent systemtomake diethylketone, a marked stability of the catalyst results. Owing to the increased stability of the catalyst, the catalyst solution can be used repeatedly by simply separating the unreacted gases and diethylketone from the reaction product by distillation after completion of the reaction.

As typical rhodium compounds available for this invention, the following compounds are exemplary: rhodium oxides, rhodium halogenides, rhodium carbonyls, rhodium hydride complexes, rhodium complexes having ligands such as triphenylphosphine and triphenyl arsine and a mixture thereof, for example, Rh O RhCl .3I-I O, Rh (CO) Rh (CO) RhCl l( 6 5)3 ]3 )2]2 6 )3 )2-( )2]2 RhCl(CO)[(C I-I P] and RhI-I(CO) [(C H P] etc.

Organophosphorous compounds employed in this invention are (CH C I-I P, (C I-I P, (CH CH O) P, (CI-I C I-I O) P, (CI-I CI-I CI-I CI-1 O) P and (C H O) P, etc. These compounds correspond to those having the infrared A carbonyl stretching frequency of Ni(CO) L (L is an organophosphorous compound) in methylene chloride as is defined by Tolman (JACS, 92, 2953 (1970)) in the range of above 2066 cm. Among organophosphorous compounds available for inhibiting the forming of high boiling substances are those of having the A carbonyl stretching frequency of Ni(CO) L in methylene chloride in the range of from 2,066 to 2,072 cm. For example, the following compounds are within the above range: (CI-I C H P, 6 5)2( 3 2) a 6 5)2( 6 5 2) 6 5)3 a 6 5)2( 6 4 s and G s)2( 3 These phosphorous compounds may be used in the form of an isolable rhodium complex containing phosphorous ligands, and also may be added to rhodium compounds without phosphorous ligands. In the latter case, these phosphorous compounds are preferably added in the range of l 10 moles per gram atom of metallic rhodium.

A rhodium compound as the catalyst may be added in amounts from 0.01 to 1% by weight calculated as metal base on ethylene.

Among alcoholic solvents used in this invention are included aliphatic monohydric or polyhydric alcohols and alcohols having polar groups other than hydroxyl group. Illustrative are, for example, methanol, ethanol, isopropanol, cyclohexanol, 2-ethylhexanol, ethanolamine and ethyleneglycol etc.

The quantity of water added can be widely varied in the range of from a stoichiometric amount necessary for the forming of diethylketone to an amount suitable for dissolving the catalyst homogeneously. I

In addition to the solvents above, any inert solvents such as n-hexane, benzene, cyclohexane and tetralin, etc. may be used as a diluent.

The reaction of ethylene and carbon monoxide may be performed in a batchor continuous system with a pressurized reactor. The reaction temperature may be in the range of 100 300C, preferably of 140 250C.

Carbon monoxide is maintained in the range of 0.1 3.0 in molar ratio to ethylene, and the reaction pressure may be kept in the range of 10 300 Kg/cm in total pressure, and of particular advantage in the range of 30 200 Kglcm Some of preferable embodiments according to this invention are described more in detail hereinunder, but it should be understood that these will not limit this invention so far as these are within the scope and spirit of this invention.

EXAMPLES 1 2 In an autoclave of 50 cc capacity 21 mg of Rh (CO) and a solvent were placed. Ethylene was introduced therein at an ordinary temperature to pressurize to 25 Kglcm followed by feeding under pressure of carbon monoxide to Kglcm The reaction was carried out at 170C. for 3 hr. The results were shown in Table 1.

Table 1 Selectivity Conversion to No. of of ethylene Diethylketone Example Solvent (mole (wt%) Comparative Example 1 Water 20 ml 18 82 2 methanol 20 ml 8 46 Example 1 methanol 20 ml,

water 2 ml 60 86 2 ethanol 20 ml,

water 2 ml 49 88 EXAMPLES 3 6 In an autoclave of 50 cc capacity was placed 100 mg of RhI-I(CO) [P(C H which was prepared from RhC1 L3H O in accordance with the method of Wilkinson et al. [1. Chem. Soc., (A), 2660 (1968)]. After the addition of a solvent, ethylene was charged under pressure therein at an ordinary temperature to 25 Kglcm and subsequently carbon monoxide introduced under pressure to 50 Kglcm The reaction was carried out at 170C. for 3 hr. The results were tabulated in Table 2.

Table 2 Selectivity Conversion to Dieth- No. of of ethylene ylketone Example Solvent (mole wt Comparative Example 3 acetic acid 20 ml,

water 2 ml trace 4 acetone 20 ml,

water 2 ml 4 -l00 5 tetrahydrofuran 20 ml,

water 2 ml 7 91 6 methanol 20 ml 2 -l00 7 isopropanol 20 ml 8 -l00 8 water 20 ml 5 Example 3 methanol 20 ml,

water 2 ml 32 91 4 isopropanol 20 ml,

water 2 ml 23 93 5 Z-ethylhexanol 20 ml,

water 2 ml 31 6 ethanolamine 20 ml,

water 2 ml 21 93 From the table, it will be seen that the conversion of ethylene was very high in the alcohol-water solvent system, compared with that in any other solvents, and that I .1 6 diethylketonewasfforme'd ith good selectivity. In complex having the same organophosphorous ligand. comparative Example .7, acetone, which was the dehy- The organophosphorous compound may exist in the redrogen'ated ipfqdupt bfiisopropanol, was formed in.an action system as a isolable rhodium complex containing amountequivalenfito that of the diethylketone formed, organophosphorous ligands.

whereas in.Examplef4'hardly any acetone was formed. The results from Examples 1 l 14 clearly show that Thus wasiaffirlmedtliat the hydrogen required for the the forming of high boiling materials is greatly deform ng of diethylketone' was supplied from the water pressed by the addition of an organophosphorous comrather than from the'alcohol in the water-alcohol sys pound having the A carbonyl stretching frequency of tem. 0 'Ni(CO) L (L is a phosphorous ligand) in methylene a Y l chloride in the range of from 2,066 2072 cm.

EXAMPLE 7 i In these Examples, almost all of the product formed To an autoclave of 100 cc capacity were added 100 consist of diethylketone, excepting high boiling submg of Rh' O 40 ml of ethanol and ml of water. Ethstances and a very small amount of propionaldehyde. ylene was supplied forcibly in the autoclave at an ordinary temperature, and the pressure was increased to 40 EXAMPLE l7 Kg/cm. Then, carbon monoxide was introduced under In an autoclave of 100 cc capacity was placed 0.05 gr pressure therein to 75 Kg/cmi, and the reaction was of Rh(CO) [P(C H and 40 ml of methanol and 4 conducted at 2()0C.'for 2 hr. 70 mole of ethylene ml of water were added therein. Ethylene was fed was reacted, and diethylketone was obtained with a seunder pressure into the autoclave at an ordinary temlectivity of 85 wt perature to 37 Kg/cm and carbon monoxide was then forcibly introduced to 60 Kg/cm The reactants were EXAMPLE 8 heated to 200C. with stirring. The reaction was contin- To an autoclave of 100 cc were added 100 mg of ued for 5 hr. maintaining the pressure at 80 Kg/cm by RhCltCO) [As(C,,l-l 40 ml of methanol and 4 ml making up carbon monoxide about every 1 hour. 40 of water, and ethylene was supplied therein at an ordimole of ethylene was reacted in this manner. This nary'tempe rature, and was pressurized to 40 Kg/cm corresponds to conversion of 1,500 moles of ethylene followed by introducing carbon monoxide under presper one gram atom of rhodium. Diethylketone sure to 7-5, Kg/cm The reaction was carried out at amounted to 97% by weight of the reaction products. 140C. for 3 hr. 62 .mole of ethylene took part in the As by-products, 3% of high boiling materials and trace reaction, and diethylketone was obtained with selectivof propionaldehyde were formed.

y Wt I EXAMPLE 18 P 30 mg of Rh,, co and 135 mg of triphenylphos- A rhodium compound amounting to 0.1 l milligram phine were placed in an autoclave of 300 cc capacity, atom'calculated :as a metallic rhodium was put in an auand 150 ml of 2-ethylhexanol and 10 ml of water were toclave of cc capacity, and' 20 ml of methanol and 2 added therein. Ethylene was filled under pressure ml of water :were' added therein. Ethylene was filled therein at an ordinary temperature to 50 Kg/cm and under pressure at an ordinary temperature to 25 subsequently carbon monoxide was introduced in the Kg/cm' and subsequently carbonmonoxide was introsame way to reach Kg/cm The reaction was carried duced under pressure to 50 Kg/cm The reaction was 40 out at 200C. with stirring. Carbon monoxide was made performed at 170C. for 1.5 hr. The results were sumup at an interval of 30 min. so as to maintain the presmarized in Table 3. The rhodium complexes having orsure at 120 Kg/cm The reaction was continued for 4 ganophosphorous ligands such as Rh(CO) [(C H P] hr. Ethylene amounting to 49% took part in the reacwere prepared in accordance with the method of Wiltion. This corresponds to the consumption of 2800 kinson et al., as described in Examples 3 6. The reac- 45 moles of ethylene per one gram atom of rhodium. Dietion time was made shorter and the reaction was carthylketone was thus obtained with selectivity of 93 wt ried under the mild conditions in order to make a comparison of the reaction rate.

Table 3 Phosphorous Compound Conversion High P/Rh of Boiling No. of (molar vC=O* Ethylene Substances Example Catalyst Compound ratio) (cm) (mole 7:) (wt 71) 9 Rh,(CO)|: nil l6 l4 l0 RhH(COM(CH,.CH CH CH ),,P],nil 2060.3 10 24 ll RhJCOlm (CH3CH4),1P 2 2066.7 26 4 12 RhH(CO)I(C,,H,,) P1 nil 2068.9 28 3 13 RhaCOm (C.,H,,);,P 3 2068.9 35 3 l4 Rh (CO) (C H -,)2(CH CH O)P 3 2071.6 33 3 l5 Rh,(C0).- (CH CH CH CH O) -,P 3 2075.6 37 10 16 RhH(CO)l(C,.-H ,0)=\P 1. nil 2085.3 39 12 A, carbonyl-stretching frequencies of Ni(CO);,L in methylene chloride (L is a phosphorous ligand).

As is seen from the comparison of Examples 9 and 10 EXAMPLE 19 with examples 1] 16, the reaction rate is increased by To mg of Rh (CO) and 410 mg of triphenylthe addition of an organophosphorous compound hav- 65 phosphine in an autoclave of 300 cc capacity were ing the A carbonyl stretching frequency 0f Ni(CO) L added ml of 2-ethylhexanol and 12 ml of water. (L is a phosphorous ligand) in methylene chloride in Ethylene was charged under pressure therein at an orthe range of above 2066 cm or by using a rhodium dinary temperature to reach 50 Kg/cm followed by introducing under pressure carbon monoxide until the pressure reached 75 Kg/cm The contents of the autoclave was heated to 200C. with stirring. When the pressure of the reaction system was reduced below 120 Kglcm carbon monoxide was supplied every 30 min. in order to maintain the pressure at 120 Kg/cm and the reaction was continued for 3 hr. After the completion of the reaction, the autoclave was cooled to room temperature to draw out the unreacted gases. Then the autoclave was heated to l C. to distill off diethylketone. To the autoclave were added water, ethylene and carbon monoxide in the same way as described above, and the reaction was conducted under the same conditions as the above. Although this operation was repeated five times, the catalyst maintained good activity in the last reaction. All of the reaction products were combined and fractionated to obtain 146 gr. of diethylketone.

What is claimed is:

1. A method for producing diethylketone with in creased formation velocity for reacting ethylene with carbon monoxide at a temperature of 100 300C., a pressure of 10 300 Kg/cm and in a alcohol-water solvent system, said alcohol selected from the group consisting of lower saturated aliphatic monohydric alcohols and ethyleneglycol, in the presence of a combined catalyst system of a rhodium compound selected from the group consisting of rhodium oxide, rhodium halogenide, rhodium carbonyl, rhodium complexes having ligands selected from the group consisting of triphenyl phosphine, triphenyl arsine and mixtures thereof, and an organophosphorous compound having an infrared A carbonyl stretching frequency of Ni(- CO) L (L represents the organophosphorous combased on ethylene,

3. The method of claim 1 wherein said organophosphorous compound is selected from the group consisting of (CH C H P, (C H P, (CH CH O) P, (CH C l-l O) P and (C H O) P.

4.'The method of claim 1 wherein said rhodium compound is selected from the group consisting of Rh O RhCl 3H O, Rh (CO) Rh (CO), 6 5)3 ]3, )z]2, 6 5)3 )2-' )2]2, [(C6H5)3P]2 and s 5)3 ]3' 5. The method of claim 1 wherein said alcohol is selected from the group consisting of methanol, ethanol, isopropanol, cyclohexanol,2-ethylhexanol, ethanolamine, and ethyleneglycol.

6. The method of claim 1 wherein said rhodium compound is used in an amount of from 0.01 to 1 weight percent, calculated as rhodium metal based on ethylene.

7. The method of claim 1 wherein said rhodium compound is selected from the group consisting of Rh O 3- 2 4( )12. 6( )16, s 5)a ]3, )2l2, s 5)a )2-( )z]2. K [(C6H5)3P[2, and [(C6H5)3P]3, the organophosphorous compound is selected from the group consisting of (CH C H P, (CH CH (C H P, a 5 m) a -M2 (C6H4F) 6 5)2 s 5)a and (CH O) (C l-l P, and wherein said alcohol is selected from the group consisting of methanol, ethanol, isopropanol, cyclohexanol, Z-ethylhexanol, ethanolamine, and ethyleneglycol.

8. The method of claim 6 wherein the organophosphorous compound is employed in the range of 1 to 10 moles per gram atom of metallic rhodium, wherein the rhodium compound is used in an amount of from 0.01 to 1 weight percent calculated as metallic rhodium the reaction temperature is l40-250C., and the reaction pressure is 30-200 kglcm 9. The method of claim 7 wherein the carbon monoxide to ethylene molar ratio is in the range of 0.1 to 3.0. 

1. A METHOD FOR PRODUCING DIETHYLKETONE WITH INCREASED FORMATION VELOCITY FOR REACTING ETHYLENE WITH CARBON MONOXIDE AT A TEMPERATURE OF 100* - 300*C., A PRESSURE OF 10 - 300 KG/CM2, AND IN A ALCOHOL-WATER SOLVENT SYSTEM, SAID ALCOHOL SELECTED FROM THE GROUP CONSISTING OF LOWER SATURATED ALIPHATIC MONOHYDRIC ALCOHOLS AND ETHYLENEGLYCOL, IN THE PRESENCE OF A COMBINED CATALYST SYSTEM OF A RHODIUM COMPOUND SELECTED FROM THE GROUP CONSISTING OF RHODIUM OXIDE, RHODIUM HALOGENIDE, RHODIUM CARBONYL, RHODIUM COMPLEXES HAVING LIGANDS SELECTED FROM THE GROUP CONSISTING OF TRIPHENYL PHOSPHINE, TRIPHENYL ARSINE AND MIXTURES THEREOF, AND AN ORGANOPHOSPHOROUS COMPOUND HAVING AN INFRARED A1 CARBONYL STRETCHING FREQUENCY OF NI(CO)3L (L REPRESENTS THE ORGANOPHOSPHOROUS COMPOUND) IN METHYLENE CHLORIDE IN ACCORDANCE WITH THE DEFINITION BY TOLMAN IN THE RANGE OF FROM 2,066 CM-1 TO 2,072 CM-1, THEREBY INHIBITING THE FORMATION OF HIGH BOILING SUBSTANCES AS BY-PRODUCTS.
 2. The method of claim 1 wherein said organophosphorous compound is selected from the group consisting of (CH3C6H4)3P, (CH3CH2) (C6H5)2P, (C6H5CH2) (C6H5)2P, (C6H4F) (C6H5)2P, (C6H5)3P, and (CH3O) (C6H5)2P.
 3. The method of claim 1 wherein said organophosphorous compound is selected from the group consisting of (CH3C6H4)3P, (C6H5)3P, (CH3CH2O)3P, (CH3C6H4O)3P and (C6H5O)3P.
 4. The method of claim 1 wherein said rhodium compound is selected from the group consisting of Rh2O3, RhCl3 . 3H2O, Rh4(CO)12, Rh6(CO)16, RhCl((C6H5)3P)3, (RhCl(CO)2)2, (Rh((C6H5)3As)2.(CO)2)2, RhCl(CO) ((C6H5)3P)2, and RhH(CO)((C6H5)3P)3.
 5. The method of claim 1 wherein said alcohol is selected from the group consisting of methanol, ethanol, isopropanol, cyclohexanol,2-ethylhexanol, ethanolamine, and ethyleneglycol.
 6. The method of claim 1 wherein said rhodium compound is used in an amount of from 0.01 to 1 weight percent, calculated as rhodium metal based on ethylene.
 7. The method of claim 1 wherein said rhodium compound is selected from the group consisting of Rh2O3, RhCl3.3H2O, Rh4(CO)12, Rh6(CO)16, RhCl(C6H5)3P)3, (RhCl(CO)2)2, (Rh((C6H5)3As)2.(CO)2)2, RhCl(CO) ((C6H5)3P(2, and RhH(CO) ((C6H5)3P)3, the organophosphorous compound is selected from the group consisting of (CH3C6H4)3P, (CH3CH2) (C6H5)2P, (C6H5CH2) (C6H5)2P, (C6H4F) (C6H5)2P, (C6H5)3P, and (CH3O) (C6H5)2P, and wherein said alcohol is selected from the group consisting of methanol, ethanol, isopropanol, cyclohexanol, 2-ethylhexanol, ethanolamine, and ethyleneglycol.
 8. The method of claim 6 wherein the organophosphorous compound is employed in the range of 1 to 10 moles per gram atom of metallic rhodium, wherein the rhodium compound is used in an amount of from 0.01 to 1 weight percent calculated as metallic rhodium based on ethylene, the reaction temperature is 140*-250*C., and the reaction pressure is 30-200 kg/cm2.
 9. The method of claim 7 wherein the carbon monoxide to ethylene molar ratio is in the range of 0.1 to 3.0. 